CREDIT FACILITY - Old and New Credit Facility (Details) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Credit Facility
Face amount of debt	$ 1,293,405	$ 1,279,188
Debt issuance costs	634
Loss on extinguishment of borrowings	(6,094)
Contingent Principal Payments		0
Contingent principal payments due in current year	0
Deferred financing costs	$ 8,297	$ 9,645
Credit Facility
Credit Facility
Actual total secured leverage ratio	3.85
Consolidated EBITDA	$ 326,602
Secured leverage ratio threshold for contingent principal payments		3.75
Credit Facility \| Maximum
Credit Facility
Actual total secured leverage ratio	6.25
First Lien Term Loan
Credit Facility
Face amount of debt	$ 1,153,000
Quarterly installment repayments	2,891
Debt issuance costs	634
Loss on extinguishment of borrowings	6,094
Write-off of debt issuance cost	5,306
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net, Total	$ 788
First Lien Term Loan \| LIBOR
Credit Facility
Margin (as a percent)	2.00%
First Lien Term Loan \| Base rate
Credit Facility
Margin (as a percent)	1.00%
First Lien Revolver
Credit Facility
Accordion feature	$ 650,000
Maximum borrowing capacity	$ 30,000
Unused commitment fee (as a percent)	0.50%
Deferred financing costs	$ 8,297	$ 9,645
First Lien Revolver \| LIBOR
Credit Facility
Margin (as a percent)	2.00%
First Lien Revolver \| Base rate
Credit Facility
Margin (as a percent)	1.00%
First Lien Revolver Step Down One
Credit Facility
Unused commitment fee (as a percent)	0.375%
First Lien Revolver Step Down One \| LIBOR
Credit Facility
Margin (as a percent)	1.75%
First Lien Revolver Step Down One \| Base rate
Credit Facility
Margin (as a percent)	0.75%
First Lien Revolver Step Down Two
Credit Facility
Unused commitment fee (as a percent)	0.25%
First Lien Revolver Step Down Two \| LIBOR
Credit Facility
Margin (as a percent)	1.50%
First Lien Revolver Step Down Two \| Base rate
Credit Facility
Margin (as a percent)	0.50%
First Lien Revolver Step Down Three \| LIBOR
Credit Facility
Margin (as a percent)	1.25%
First Lien Revolver Step Down Three \| Base rate
Credit Facility
Margin (as a percent)	0.25%

Actual total secured leverage ratio maintained by the company.

No definition available.

Name:	focs_ActualTotalSecuredLeverageRatio
Namespace Prefix:	focs_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of consolidated earnings before before interest, taxes, depreciation, and amortization.

+ References

No definition available.

+ Details

Name:	focs_ConsolidatedEarningsBeforeInterestTaxesDepreciationAndAmortization
Namespace Prefix:	focs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contingent principal payments due.

+ References

No definition available.

+ Details

Name:	focs_ContingentPrincipalPayments
Namespace Prefix:	focs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of contingent principal payments due in current year.

+ References

No definition available.

+ Details

Name:	focs_ContingentPrincipalPaymentsCurrentYear
Namespace Prefix:	focs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of accordion feature in Line of Credit Facility.

+ References

No definition available.

+ Details

Name:	focs_LineOfCreditFacilityAccordionFeature
Namespace Prefix:	focs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The First Lien Leverage Ratio that the entity must not equal or exceed without being subject to contingent principal payments based on excess cash flow, as defined in the Credit Facility.

+ References

No definition available.

+ Details

Name:	focs_SecuredLeverageRatioThresholdForRequiredContingentPrincipalPayments
Namespace Prefix:	focs_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12355-112629

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12317-112629

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainsLossesOnExtinguishmentOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of the required periodic payments of both interest and principal.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityPeriodicPayment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3291-108585

+ Details

Name:	us-gaap_PaymentsOfDebtIssuanceCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

Name:	us-gaap_WriteOffOfDeferredDebtIssuanceCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=focs_FirstLienTermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=focs_FirstLienRevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=focs_FirstLienRevolverStepDownOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=focs_FirstLienRevolverStepDownTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=focs_FirstLienRevolverStepDownThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: